Cathode sealing means for electrolytic cell



April 16, 1963 G. T. MoTocK 3,085,968

cATHoDE SEALING MEANS FOR ELEcTRoLYTIc CELL GEORGE T. MOTOCK CKMM'ATTORN YS April 16, 1963 G. T. MoTocK CATHODE SEALING MEANS FORELECTROLYTIC CELL 9 Sheets-Sheet 2 Filed Aug. 16, 1960 INVENTOR. GEORGE'l'. MOTOCK Wwf ATTORN YS April 16, 1963 G. T. MoTocK 3,085,963

CATHODE SEALING MEANS FOR ELECTROLYTIC CELL Filed Aug. 16, 1960 9Sheets-Sheet 3 f if@ #-120 ,i IIL'. 05m* INVENTOR.

GEORGE T. MOTOCK ATTORNE S April 16, 1963 G, T M01-@CK 3,085,968

CATHODE SEALING MEANS FOR ELECTROLYTIC CELL INVENTOR. GEORGE T. MOTOCKATTORNEYS April 16, 1963 G. T. MoTocK CATHODE SEALING MEANS FORELECTROLYTIC CELL 9 Sheets-Sheet 6 Filed Aug. 16, 1960 looo FIG. I7

Fucile INVENTOR GEORGE T. MOTOCK BY mZww/*Zk f EYS ATTOR April 16, 1963.G. T. MoTocK 3,035,968

CATHODE SEALING MEANS FOR ELECTROLYTIC CELL Filed Aug. 16, 1960 9Sheeis-Sheet '7 INVENTOR. GEORGE T. MVOTOCK ATTORNEYS April 16, 1963 G.T. MoTocK 3,085,968

CATHODE SEALING MEANS FOR ELECTROLYTIC CELL Filed Allg. 16, 1960 9Sheets-Sheet 8 120e |203 INVENToR.

|204 GEORGE T MoTocK BYl y Wy'mf ATTORNEY April 16, 1963 G. T. MoTocKCATHODE SEALING MEANS FOR ELECTROLYTIC CELL Filed Aug. 1s, 1960 9Sheets-Sheet 9 5 2 mw F INVENTOR. GEORGE T. MOTOCK ATTORNEYS UnitedStates Patent Hlfce 3,085,963 Patented Apr. 16, 1963 3,085,968 CATHODESEALING MEANS FOR ELECTROLYTIC CELL George T. Motock, Hamden, Conn.,assignor to Olin Mathieson Chemical Corporation, `a corporation ofVirginia Filed Aug. 16, 1960, Ser.` No. 49,972 4 Claims. (Cl. 204--247)'This invention relates to improvements in the design of cells used forIthe production of `alkali metals, e.g., sodium :and lithium, Ibyelectrolysis of a -fused salt. In particular, this invention relates toa novel cathode and novel sealing means for cathodes for such fused saltcells.

In the operation of `fused salt cells, a fused salt mixture iselectrolyzed to produce alkali metal at the cathode and halogen gas atthe anode. The anode is conventionally a cylindrical graphite or carbonanode surrounded -by an annular metallic cathode. A porous ydiaphragm isprovided in the anode-cathode annular space to assist in the separationof the products of electr-olysis.

The fused salt electrolyte 'bath is very corrosive, particularly a fusedmixture of lithium chloride and potassium chloride used to producelithium, and due to the high temperature of operation serious problemsof leakage of the molten electrolyte are present, particularly aroundthe cathode arms when the cathode is'the type with opposed side armsextending through the cell side walls. Leakage of electrolyte can causeshut-downs in cell operations. Also, an electrically insulated seal mustbe provided for the cathode -ar-ms extending through the shell of thecell.

rlhis invention provides -a novel side entrant cat-hode and sealingmeans for the cathode which effectively insulates the cathode from thecell shell and prevents the molten electrolyte from leaking past thecathode arms. To accomplish this, the cathode side arms are providedwith passages for conducting -a coolant through the portion of the armextending through the cell. Also, an enclosure or receptacle is providedon the cell wall exterior for containing castable refractory materialthrough which the side arm of the cathode extends in contact with thecastable refractory material. `On the por-tion of the side arm withinthe enclosure, a dam is attached which is in contact with the refractorymaterial. 'The cell side wall is refractory-lined and -t-he side armrests on the -refractory which also serves as electrical insulation. Theopening in the exterior end of the enclosure is langer than the cat-hodearm so that no electrical contact is made with the enclosure.

The cooled side arm freeze any leaking electrolyte and thus, tends toprevent further leakage. The enclosure with refractory and the dam onlthe side arm., which provides -a tortuous path for -leakingelectrolyte, effectively prevents leakage of molten electrolyte,particularly when cooled side arms are used which freezes anyelectrolyte in the enclosure.

The invention will be further illustrated by reference to theaccompanying drawings which illustrate a fused salt electrolysis cellwith four anodes and cathodes and designed for operation at `30,000amperes and for the production of lithium from a mixture of lithiumchloride and potassium chloride.

'FIGURE 1 is a plan view of the fused salt electrolysis cell with thecover removed.

FIGURE 2 is a view of the section taken along 2-2 of FIGURE l. y

FIGURE 3 is a side view of one of the anodes of FIGURE 1.

FIGURE 4 is a cross-sectional view of the anode sealing means of FIGUREl.

FIGURE 5 is a plan view of the anode connector of FIGURE 1.

FIGURE 6 is a front view of the anode connector of FIGURE 1..

FIGURE 7 is an end view of the anode connector of FIGURE l.

FIGURE 8 is a cross-sectional view taken through 8 8 of FIGURE 5,showing a typical water-cooled area.

FIGURE 9 is a plan view of the cathode assembly of FIGURE l, showing theanodes and diaphragme in place.

FIGURE 10 is a front elevation view of the cathode assembly of FIGURE 9.

FIGURE 11 is a side elevation view of the cathode yassembly of FIGURE 9.

FIGURE i12 is a detail of the dam of FIGURE 9.

.FIGURE d3 isa plan view of the assembly of FIGURE 1 for collecting theproducts of electrolysis.

FIGURE 14 is a sectional view taken through 14-14 of FIGURE 13.

FIGURE 15 is a sectional view taken through 15-15 of FIGURE 13.

FIGURE 16 is a cross-sectional view of a pilot post of FIGURE Il. Y

FIGURE 17 is a plan view of the chlorine dome of FIGURE 1.

FIGURE 18 is a cross-sectional view taken through 18-18 of FIGURE 17.

FIGURE 19 is a plan view of the lithium metal riser and overflow pipeassembly of FIGURE 1.

FIGURE "2()l is a cross-sectional view taken through 20--20 of FIGURE19.

FIGURE 2l is a cross-sectional view taken through 21-21 of FIGURE 20.

FIGURE 22. is a cross-sectional view taken through Z2- 22 of FIGURE 20.

FIGURE 23 is a plan view of the holding tank of FIGURE 1.

FIGURE 24 is a cross-sectional view taken through 24-2'4 of FIGURE 2.3.

FIGURE 25 is a plan view of the valve seat of the holding tank ofFIGURES 23 and 24.

FIGURE 26l is a cross-sectional and front elevation view ofthe valveseat taken along 26-26 of FIGURE 25.

FIGURE 27 is -a partial bottom view of the valve seat of FIGURE 25.

In the drawings, and as shown generally in FIGURES l and 2, the `basiccell structure is formed Vfrom metal and refractory material and thecell contains four bottom entrant cylindrical anodes 200, for whichanodes sealing means 300 are provided, as well as anode connectors 400for supply of electrical energy. The anodes are surrounded by anassembly of four cathodes 500 with opposed side arms. A porous diaphragm600 is positioned between each cathode and anode. A collecting assembly700 for collecting chlorine and lithium metal products is positionedabove the cathode-anode area and is supported by a collector assemblysupport 800 and positioned'and aligned by pilot posts 900. Chlorine isrecovered by means of dome 1000 and lithium metal :by means of riser1100 and holding tank 1200.

The cell 100, as shown particularly in FIGURES 1 and 2, is formed froman outer cylindrical shell of steel 101 lined with refractory material102, eg., extruded acid proof 4brick or power pressed brick. The 'bottomof the cell is formed from a circular steel table 103 lined withrefractory material, e.g., brick 104, insulated from the ground by fourporcelain insulators 105. The table 103 extends beyond the outer shell101 and a metal `dam 106 is placed on the outside rim of the cellbottom. This is lilled and rammed with castable refractory material 107sloping upwards to the cell shell to a height above the bottom of thecell. This forms a seal with the flange 108 on the Vbottom of the cellto prevent molten electrolyte leakage. Also, high density monolithiccastable refractory cement material 109 is used over the refractorybrick to form the bottom lining or floor of the cell. Vertical steelsupports 110 and horizontal beams 111 are provided to support the cellbottom. The top of the cell is formed from steel plate 111 lined withrefractory material, e.g., brick y102.

The anodes 200 are cylindrical, solid, graphite anodes and contain, asshown particularly in FIGURE 3, spaced slots 201 in the area adjacentthe cathode. As shown in FIGURE 9, the slots do not extend through tothe center of the anode. Preferably, the slots extend to only aboutone-third of the diameter of the anode. The anodes of this particularcell are sixteen inches in diameter with twenty-four slots, each slotbeing one-eighth inch wide and two inches deep. Also, an anode withtwelve slots, each slot being one-quarter inch wide and two inches deepcan be used. 'Ihe twelve slot anode is faster and easier to machine.Each anode is machinedfrom dense graphite with an overall length ofsixty-eight inches. The slots extend twenty-three inches downward fromthe top of the anode. 'Ihe slotted, solid anode provides decreasedresistance to chlorine ilow in the anode compartment of the cell,increased ion distribution in the cathode-anode annular space and lowvoltage drop across anode to cathode.

The anode is provided with a portion of reduced diameter 202 at thelower end thereof forming a shoulder 203 to facilitate supporting andsealing the anode, electrically and mechanically. In the particular cellillustrated, the lower twenty inches of the anode is reduced to a teninch diameter.

The supporting and sealing means 300 for the anodes, as shownparticularly in FIGURE 4, comprises the shoulder 203 of the anode 200which rests on an insulating ring 301 inside a squared metal, e.g.,steel, enclosure, e.g., a box or pan-like section 302 attached to thecell bottom 103. The ring 301 serves to insulate electrically the panfrom theanode. The box is concentrically located beneath a circularsteel cell bottom. The box is divided into four quadrants eachcontaining an opening for the anode. The portion of the anode of reduceddiameter 202 passes through the opening in the box section 302 and theopening is sealed by means of a metal sealing ring 303 between theinsulating ring 301 and the pan bottom 304 and a packing gland 305. Thegland 305 is adapted to hold packing 306 tightly against the anode andsealing ring 303 by means of bolts 307 engaging the gland, cell bottomand sealing ring. The anode is sealed in the cell bottom and box bymeans of refractory material 30S, e.g., refractory brick. In the cellillustrated, the insulating ring 301 serving as electrical insulationbetween the anode and steel shell is a threequarter inch thick transitering with an outside diameter equal to that of the upper anode portionand an inside diameter slightly larger than the lower anode portion.Special quadrant refractory 308 brick, four inches thick, are laid asiill for the anode box to seal the anode in the box. They are laid threehigh with refractory cement as a filler. The cell floor 109 of castablerefractory material is laid to a ydepth of two inches over the quadrantbrick. After drying, the cell and packing gland are tightened tocomplete the anode seal. The sealing means effectively prevents escapeof molten electrolyte around the anode and at the same time provides foreasy removal and replacement of the anode without destruction of thecell floor.

Electrical energy is supplied to the anodes by means of anode connectorsor clamps 400, as shown particularly in FIGURES 5 to 8. The clampcomprises two opposed metal sections 401 each having a semi-cylindricalinterior surface 402 for fitting around the external portion of thecylindrical anode, bolts 403 for holding the sections 401 together andthe interior surfaces tightly against the anode surface, passages 404with pipe connectors (bushings) 405 within each section for the flow ofcoolant through the sections and studs 406 for connection to buses. Thecooling of the clamp cools the lower portion of the anode and alsofreezes any molten electrolyte that may leak around the anode seal.Also, the coolant aids in reducing expansion of the metal partspreventing loosening of the connection. A copper bus is attached to eachhalf of the clamp by means of the four studs 406 and a four sided framewhich bolts the bus tightly to the clamp. The clamp is preferably madefrom silicon bronze rather than mold steel because of the compatibilityof silicon bronze and copper bus connections and also because of itshigh resistance to corrosion as well as high strength. The sections 401can be machined from solid stock or cast and partially machined. Theportions of the clamp facing the graphite anode (surfaces 402) andcopper bus (surface 407) are plated with silver to insure `goodelectrical contact. In the particular clamp illustrated, the clamp, whentightened, forms a ten inch diameter by ten inch high sleeve and faces1130.4 inches of graphite, giving a current density of 26.54 amperes persquare inch at 30,00() amperes.

The cathode assembly 500 includes cylindrical steel cathode sleeves orrings 501 ooncentrically surrounding each anode and having opposed steelside arms 502. As shown particularly in FIGURES l and 2 and 9 to l2, theside arms 502 of the illustrated cell support the group of four cathodecylinders 501. The walls of the cathode cylinders are solid. In theparticular cell illustrated, the inner `diameter of the cathode ring isnineteen inches. The anode-cathode spacing is one and one-half inches.The side arms 502 rest on the refractory brick lining of the cell walland extend through the outer shell of the cell and are machined andsilvered to accommodate a copper bus which is clamped to the arm in amanner similar to the anode by means of studs 503. The side arms areprovided with passages 504 for flow of coolant. FIlle side arms areinsulated and sealed against electrolyte leakage by means of a metal, e.g., steel, enclosure or box 505 mounted on the side of the cell shellthrough which box the side arms pass (see FIGURES l and 2). The boxcomprises four walls 506 attached to the cell shell 101 and a side plate507 bolted to the walls 506. A metal dam or dike 508 is welded to theside `arm 502 so that the dam 508 is approximately centrally locatedwith the box 505. After the brick shell is built around the cathodearms, castable refractory cement 509 is rammed and packed into the boxso ythat it is in tight contact with the cell and box walls and sidearms and the dam thereon. The castable refractory material and dameffectively prevent the molten electrolyte from leaking through thecathode seal. The dam also can be in the shape of a U. Also, anadditional dam can be attached to the inside of the box to provide amore tortuous path for the electrolyte and prevent its leakage. Also,the coolant in the cathode side arm serves to freeze any moltenelectrolyte leaking into the box and thus aids the seal. The side plate507 has an opening 510 through which the cathode arm passes withoutcontacting the plate. The opening is designed to leave a gap around `thecathode side arm to insure against electrical contact between the armand the metal shell of the cell. Thus, the cathode side arm is incontact only with refractory material which serves as insulation.

The diaphragms 600 are cylindrical sleeves positioned in the areabetween each anode 200 and cathode sleeve 501. The preferred diaphragm,as shown in detail in FIGURE 14, is a perforated metal sheet, althoughother types made from porous ceramic materials, e.g., alumina, magnesiaor other oxides non-reactive with the electrolysis products, or metalwire screens can be used. The metal sheet can be carbon steel orstainless steel or at least twenty-four gauge thickness. The importantfeature of the diaphragm is the percentage of open area.

The open area required varies with the electrolysi-s conditions, i.e.,the composition, temperature and viscosity of the molten salt mixture(electrolyte) employed. An open area of about 30l toy 50 percent hasbeen found to be satisfactory for the illustrated cell. In theparticular cell illustrated, the preferred diaphragm is a cylinder oftwenty-four gauge perforated stainless steel (type 304 or 316) sheet ofan inner diameter of seventeen inches and an overall length oftwenty-four and one-quarter inches. The perforations are 0.038 inch indiameter, 0.05 on centers both ways giving 400 openings per square inchor 45.5 percent open area straight-line pattern. In another example, theopenings are 0.038 diameter, 0.0 0.057" center with 351 openings persquare inch or 39 percent open area. The dimensions of a 26 gauge, 306grade stainless steel used are 0.30 inch diameter openings, about 225holes per square inch or 36 percent open area. The actual shape of theopenings is not important. A 0.020 inch thick sheet with slits 0.016inch wide by 0.140 inch long can be used as a diaphragm. The stainlesssteel diaphragm is better than one made of carbon steel because carbonsteel requires a thicker gauge for strength and rigidity similar to thatof stainless steel. A wire :diaphragm of carbon steel is unsatisfactorydue to buckling in operation. The diaphragm is suspended `from thechlorine and metal collecting assembly 700 by means of machined metaladapter ring 601 tting inside the upper end of the diaphragm and weldedthereto. The ring 601 has a portion of reduced diameter 602 projectingabove the diaphragm and is bolted to the collecting assembly. Thisstructure is very advantageous in that it reduces the size of thecollecting assembly and thus the overall size of the cell. Also, astrengthening ring of metal 603 is attached to the bottom of thediaphragrn.

The collecting assembly 700 comprises essentially a hood with aninclined upper surface and having within the vskirts of the hoodcylinders for holding a diaphragm between an anode and cathode and forguiding anode products to a cone-shaped structure on the inclinedsurface having an opening in its top for gas discharge, while cathodeproducts are guided by the hood skirt enclosure to a discharge openingin the highest part of the inclined surface. As shown in detail inFIGURES 13 to 15, the preferred collecting assembly comprises a singlesteel unit of a large centrally located cylinder 701 (which can besquared on one section as shown) designed to collect the chlorineevolved at the anode side of the diaphragm 600 and the liquid metalformed at the cathode side of the diaphragm. Four smaller cylinders 702extend downward from the large central cylinder 701 and hold thediaphragms 600, by means of adapter ring 601, so that passages forchlorine from `all the anodes are provided. The chlorine evolved -on theanode side of the diaphragm passes yup through the smaller cylinders 702and into a cone-shaped structure 703 on top of the large cylinder whichprovides an upwardly sloping smooth surface to a -small cylinder or pipe704, preferably of stainless steel, forming an opening through which thechlorine passes to the chlorine dome 1000. Advantageously, a metalscreen or baille 709 can be placed over the chlorine outlet 704 and acalming effect is obtained which reduces salt entrainment. Theconeshaped structure on one side advantageously extends down into thesmaller cylinders 702 as shown as 705 to form an upwardly sloping smoothsurface for chlorine ow and to eliminate gas pockets. The upper surfaceof the large cylinder 701 has an inclined surface, preferably about fromhorizontal, so as to form an inverted inclined trough 706 encircling thesmall cylinders 702 and the anode-cathode area and lithium metal formedat the cathode Iside of the diaphragm flows up from the cathodes to thetrough and out through lithium metal outlet 707. As shown in FIGURE 2,the collecting structure 700 is preferably completely submerged in themolten electrolyte or melt, with the outlet pipe 704 positioned justbelow the melt line. The melt line in the chlorine dome 1000 is higherthan in the cell proper because the pressure in the dome is less thanthat in the cell proper. The pipe 704 is kept below the melt line tominimize corrosion and erosion from the hot chlorine gas. By the use ofsuitable materials, however, the pipe can project above Vthe melt line.'Ihe collecting structure effectively separates chlorine and lithium inthe electrolyte and guides them to structures for their recovery. Thecollecting structure prevents their re-combination which would result incontaminated lithium and eectively prevents entrainment of electrolytein the chlorine stream. The assembly is provided with posts 708,preferably of stainless steel, threaded to receive hangers forsuspension from the collecting assembly support 800. While the preferredhood structure is substantially cylindrical, a substantially rectangularor square hood, preferably rounded on the corners to correspond to thesmaller downwardly projecting cylinders, can be used.

The collector support 800, as shown particularly in FIGURE l, comprisesa diamond shape steel structure, positioned on top of the cell, Wih arms801 and cross pieces 002 and 004. The collector assembly is suspendedfrom the support by means of the cross pieces 804 attached to the armsS01 with bolted hanger rods 805 which thread into the collector posts708. Each end of the diamond shaped structure formed by arms 801 issupported by attachment to a pilot post 900.

The steel pilot posts 900 are attached to steel frame work 111 and 110(which also supports the cell proper) and serve through the -collectorsupport 800 Ito position and align the collector assembly 700, includingdiaphragms 600, and chlorine dome 1000. The post 900, as shownparticularly in FIGURE 16, comprises a bottom casing 901 containing apilot shaft 902 with pilot shaft guide sleeves 903 for receiving setscrews 904 for holding and positioning horizontally the pilot shaft 902.The pilot shaft 902 is insulated from the bottom casing by transite ring905 and is provided with an insulating transite cover 906 on which restsplate 907 which receives adjusting screw 908 in adjusting collar 909 ofthe pilot guide sleeve 910 on which rests top casing 911 and cover plate912. Also, set screws 913 are provided to holding guide sleeve 910. Thevertical alignment of the collector assembly, diaphragms, and dome canthus be adjusted by screw 908l and also horizontally by means of screws904, thus providing proper alignment during cell operation.

Chlorine dome or riser 1000, as shown in detail in FIGURES 17 and 18,for recovering chlorine after it is separated from the electrolytecomprises a cylindrical (e.g., about two feet diameter) shell 1001,preferably of stainless steel, lined -with refractory brick 1002 andcastable refractory 1003. At the top of the dome is a centrally locatedpipe `1004 (e.g., about eight inch diameter) providing an opening forescape of chlorine gas. yA metal cone 1005l is provided for supportingthe refractory brick and castable refractory. The refractory liningprovides eifective protection against the corrosive hot chlorine gas andany entrained melt. Flanges 1006 are provided for engagement with crosspieces 802 of the collector support structure S00. The pipe 1004 is in asteel cover plate 1007 which also contains an opening 1008 sealed bygaskets for pressure relief and an opening 1009 sealed by a glass platefor visual observation of operation. Preferably, the dome is insulate-don its exterior to prevent plugging from freezing of any moltenelectrolyte. The dome 1000 is supported from (and positioned by) thecollector assembly support 8 00 by means of cross pieces 802 engagingthe flanges 1006 (see FIGURES 1 and 2). As shown in FIGURE 2, the dome1000 is slightly raised (e.g., one and one-half inches) above thecollector 700' so that it does not rest on it in order to provide forcirculation of electrolyte.

As shown, the dome is positioned over the pipe 704 of the -collector 700and has its lower portion submerged in the melt. The pipe 704 of thecollector projects up into the shell 1001, but, as discussed above thepipe 704 should not project above the melt surface to avoid corrosionand erosion. Chlorine is passed from the dome opening 1004 into arecovery system by means of piping 1010. The cylindricalrefractory-lined dome effectively separates the chlorine in high purityof 99 percent or more with `substantially no entrainment of electrolyteand has a long operating life even under the very severe conditions. Itprovides a low, uniform gas velocity which substantially eliminatesentrainment.

The lithium metal riser 1100, as shown in detail in FIGURES 19 to 22,functions to move the lithium metal which is collected in the annularspacing (inverted inclined trough) under the collector 700, by virtue ofthe difference in specific gravity between the liquid lithium and themolten eutectic salt mixture, to the hold tank 1200. The riser comprisesa -cylinder 1101, preferably of stainless steel, with a top plate 1102and containing in its lower portion and adapted to t snugly over thepipe opening 707 for lithium metal flow from the collector 700, asmaller interior cylinder 1103, preferably of stainless steel, locatedolf-center and adjacent to one portion of the cylinder 1101 so as toprovide a semiannular space 1104 so that lithium metal flows up throughthe cylinder 1103 and into the space 1104. The smaller interior cylinder1103 extends up into the cylinder 1101 a distance sufficient to bringits top at least to the melt line and preferably at the melt line. Theriser is supported by the pipes 1105 and 1106 attached to hold tank 1200and cylinder 1101 (see FIGURE 2). Hold tank 1200 can be positionedvertically or horizontally to align the cylinders 1101 and 1103 over thecollector opening 707 and with respect to the melt level.

The lithium metal flows from the space 1104 and cylinder 1101 up throughan inverted V-shaped pipe structure, preferably of stainless steel,comprising an upwardly inclined (e.g., 45) pipe 1105 extending into thecylinder 1101 and over the edge of interior cylinder 1103. The metalflows up the pipe 1105 land then down a downwardly inclined (e.g., 60`from vertical) pipe 1106 into a holding tank 1200. At the top of theinverted V intersection of the two pipes 1105 and 1106 a blind flange1107 is provided, which can be removed to unplug the pipes 1105 and 1106through opening 1108, in the event they become plugged with frozenelectrolyte or metal. Maintaining pipe 1105 and 1106 at a temperature ofabout 300 C. by external heating helps to prevent plugging. The topplate 1102 can contain opening 1109 and pipe 1106 opening 1110 forpiping any chlorine gas evolved directly to the chlorine header 1010 toprevent recombination of chlorine and lithium and recover the chlorine.The riser can then be operated successfully without an argon pad,although argon padding can be provided if desired through opening 1111.Argon padding is used to prevent nitridation and oxidation of thelithium metal from contact with air. When chlorine is piped directly tothe chlorine header 1010' the suction on the header must be carefullycontrolled so as to prevent metal carryover into the gas line.

The riser effects a complete separation of lithium of high purity, i.e.,99 percent or more. Recombination of lithium and chlorine is virtuallyeliminated, as well as entrainment of electrolyte. After long service,the riser is exceptionally clean and free `from salt or metalaccumulation.

The holding tank 1200, `as shown in detail in FIGURES 23 and 24, isdesigned to accumulate and hold lithium metal during a cell campaign. Itcomprises a cylindrical tank 1201, preferably of stainless steel, with atop plate 1202 having an opening for inflow of lithium metal by pipe1106 from the riser 1100. The bottom 1203 of the tank is inclineddownwardly from the lithium inlet side in the refractory-lined chlorinedome.

to an opening 1204 in the opposite side for discharge of lithium metalwhich is controlled by a valve 1205, controlled by means of stem 11206from the top of the tank. Opening 1207 is provided for argon padding toprevent nitridation and oxidation of the lithium. The tank is heated bymeans of external heaters, particularly along the tank bottom, tomaintain the molten lithium at temperatures at least about 50 C. higherthan the melting point of lithium (186 C.), e.g., about 250 C. Thetemperature must be maintained evenly over the entire arca of the tankor else the lithium metal freezes, particularly in the area around theseat of valve 1205. A jacketed valve seat 1208, as shown in detail inFIGURES 25 to 27, equipped with heaters, e.g., cartridge heaters,effectively prevents such failures from freezing of lithium. The seat1208 is provided with holes 1209 4for receiving the cartridge heatersand between the heaters holes 1210 for thermocouples for controlling thecartridge heaters are provided.

In the operation of the illustrated cell, ia mixture of lithium chlorideand potassium chloride was charged to the cell to form the melt. Themixture was first subjected to a pre-electrolysis period, preferablywith alternating current, to form the molten electrolyte. Thepreelectrolysis not only removes water of hydration from the salt butalso removes the chemically bound impurities, i.e., metal hydrides andhydroxides which cannot be removed by heating alone. Following thisperiod, the electrolyzing current is applied. The composition of themolten electrolyte was maintained at about 40 to 50 percent lithiumchloride. The electrolyte temperature was maintained at about 400 to 480C., preferably about 420 to 460 C., at a current level of about 20,000to 30,000 amperes. The temperature can be maintained without theaddition of external heat. Operating conditions for optimum productionare a current level of 24,000 to 26,000 amperes, an electrolytecomposition of 46 to 48 percent lithiLun chloride, an electrolytetemperature of 450 C. and an electrolyte level of about 2 to 4 inchesfrom the top rim of the cell. Maximum current efficiency is obtained at25,000 amperes, at which level gives an anode current density of 6.55and a cathode current density of 5.51 amperes per square inch. Operatingat current levels below 24,000 or above 26,000 amperes results inreduction in current efficiency. High melt concentration causes a markedreduction in the cathode to diaphragm potential with excessive formationof surface metal. Deviation from an electrolyte temperature of 450 C.results in reduction in current elliciency. An increased amount ofcorrosion occurs on the cathode when the melt level falls below 4inches.

On electrolysis of the fused salt mixture, chlorine was formed at theanode and directed by the diaphragm to the collector assembly `andseparated from the electrolyte The lithium formed at the cathode on thecathode side of the diaphragm collected in the inverted inclined troughand flowed into the metal riser where it was separated from theelectrolyte and flowed to the holding tank, which was periodicallydrained.

The chlorine from the chlorine dome was of high purity, i.e., above 99.0percent, and the lithium metal from the hold tank was of a purity ofabout 99.5 percent, in contrast to prior lithium cells wherein for lackof adequate separating structures chlorine was not recovered and lithiumwas removed from the bath surface as a crude product containing lithiumand potassium chloride impurities.

What is claimed is:

l. In a fused salt electrolysis cell, the combination of a cathode withopposed side arms extending through refractory-lined cell side walls andresting on said refractory, the arms containing passages for conductinga coolant through the portions of the arms extending through the cellside wall, and means dening an enclosure mounted on the exterior cellside wall, said enclosure containing a castable refractory materialthrough which the side arm extends in contact with the castablerefractory material and a dam attached to the arm at a posi tion withinthe enclosure and in contact with the castable refractory material.

2. In a fused salt electrolysis cell, a cathode with opposed side armsextending through refractory-lined cell side walls and resting on therefractory, means dening an enclosure mounted on the exterior cell wall,said enclosure containing a castable refractory material through whichthe side arm extends in contact Awith the castable refractory materialand a dam `attached to the arm at a position within the enclosure and incontact With the castable refractory material.

3. The combination of claim 1 in which the enclosure is a box comprisingfour walls attached to the cell wall 10 and a side plate attached to theWalls with an opening in the side plate through which the cathode armpasses. 4. The combination of claim 2 in which the enclosure is a boxcomprising four Walls attached to the cell wall and a side plateattached to the Walls with an opening in the side plate through whichthe cathode arm passes.

References Cited in the tile of this patent UNITED STATES PATENTS12,213,073 McNitt Aug. 27, 1940 2,234,967 Gilbert Mar. 18, 19412,311,257 Sawyer et a1 Feb. 16, 1943 2,355,761 Upton Aug. 15, 19442,621,155 Williams Dec. 9, 1952 2,865,833 Renner et al. Dec. y23, 19582,887,448 Bergh et al. May 19, 1959

1. IN A FUSED SALT ELECTROLYSIS CELL, THE COMBINATION OF A CATHODE WITH OPPOSED SIDE ARMS EXTENDING THROUGH REFRACTORY-LINED CELL SIDE WALLS AND RESTING ON SAID REFRACTORY, THE ARMS CONTAINING PASSAGES OR CONDUCTING A COOLANT THROUGH THE PORTIONS OF THE ARMS EXTENDING THROUGH THE CELL SIDE WALL, AND MEANS DEFINING AN ENCLOSURE MOUNTED ON THE EXTERIOR CELL SIDE WALL, SAID ENCLOSURE CONTAINING A CASTABLE REFRACTORY MATERIAL THROUGH WHICH THE SIDE ARM EXTENDS IN CONTACT WITH THE CASTABLE REFRACTORY MATERIAL AND A DAM ATTACHED TO THE ARM AT A POSI- 